NASHVILLE, Tennessee—Gene editing can be deployed as an effective strategy to correct mutations in the human genome in an attempt to treat monogenic diseases such as Duchenne muscular dystrophy (DMD), according to Eric Olson, MD, the founding chair of the Department of Molecular Biology at the University of Texas Southwestern Medical Center in Dallas.
During his presentation at the 2022 Muscular Dystrophy Association Clinical & Scientific Conference, Dr. Olson gave an overview of the 3 different CRISPR-Cas9 gene editing approaches his team has used to correct errors in the DMD gene. These are the single-cut version of the technique that uses nucleases or molecular scissors, the second version that uses base editors, and the third version that uses prime editors.
Dr. Olson described the different mouse models that his laboratory developed of the most prevalent DMD mutations and how they used these models to confirm the efficacy of the different gene-editing approaches in correcting the expression of the dystrophin protein.
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Using the single-cut CRISPR approach, Dr. Olson and his team showed that dystrophin was restored above therapeutic thresholds and that the animals’ muscle health was maintained even following excessive exercise. However, in this approach, a double-stranded break is made in the DNA, which can be a concern.
Dr. Olson’s team, therefore, tested base editing that does not make double-stranded breaks in the DNA. In this approach, canonical splice acceptor and donor sequences are edited, making the exon they are flanking “invisible.” “We’ve adapted this approach to change a host of mutations,” Dr. Olson said. Dystrophin expression was once again restored in the skeletal muscles of the animals.
Finally, in prime editing, which also does not require a double-stranded DNA break, any collection of nucleotides can be introduced or modified within a target sequence, according to Dr. Olson. He showed that using this approach, he and his team were able to restore dystrophin expression from exon 51 deletion in human induced pluripotent stem cell-derived cardiomyocytes.
Unlike other approaches, the CRISPR-Cas9 genome editing approach can result in a dystrophin protein that is almost identical in size to the original, Dr. Olson showed.
The safety of the approach should now be further evaluated and the technique should be optimized to ensure that the editing is “turned off” when the desired change has been made, he said. Finally, the adeno-associated virus (AAV) delivery vector should be optimized, and Dr. Olson said his team is currently working on that.
Reference
Olson E. CRISPR – The next generation. Oral presentation at: 2022 Muscular Dystrophy Association Clinical & Scientific Conference; March 15, 2022; Nashville, TN.
